Some task killers do that automatically but it often provokes the opposite effect: since the system needs some apps open to work properly if you use that automatic task killers, the system will need to open them again and again, decreasing by that way the battery life.
Advanced Task Killers will help you out to kill – manually – those applications that you don’t need open. Of course there is “automatic apps kill mode” but it is configurable to avoid that performance. Nonetheless, the main strength of ATK is its manual feature. You may select those apps that you want to kill just by ticking on the list of active apps and then press the button “Kill selected apps”. That easy. In the ATK settings you may select the “Auto Start” to open automatically ATK when you restart your phone. Moreover, you may choose to show or to hide an ATK icon on notification bar, set the action for selecting apps in the list (select/unselected, kill, ignore, etc.),and for long press. You may create and modify “Ignore Lists” including those apps that you don’t want to kill ever. Finally, you will be able to set the Auto Kill level (that’s it the automatic ATK mode) or its Security Level.
This is the free version of ATK for Froyo with ads. There’s also a paid version which is the same but with no ads ($4.99).
Advanced Task Killer Froyo is developed by ReChild who are the developers of other Android task manager in the Market.
ATK is a really useful tool, a must if you are one of those user who want to save battery-life by killing processes easily. Some users consider that this kind of apps are useless since the Android OS manages efficiently its resources. It’s up to you, but what it is a common place it is that ATK does it fast and easy.
It does exactly what it's supposed to do. I've been using it the last year or two. Love keeping the widget on my home screen to quickly kill tasks. Huge battery saver.